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n a recent chemical plant project for which the author was the Engineer of Record, an electrical contractor, contrary to contract specifications, manually arc welded electrical grounding conductors to reinforcing steel for a pipe rack foundation. The electrician explained that the National Electric Code (NEC) allows welding to concrete encased reinforcing steel, and he frequently does so in lieu of independent electrical ground rods which were specified on this project. Paragraph 250.52 (A) (3) Concrete-Encased Electrode of the NEC does permit welding to reinforcing steel. However, NEC does not reference AWS D1.4/ D1.4M Structural Welding Code-Reinforcing Steel or provide any guidance to the special rules, regulations, and procedures prescribed by AWS D1.4/ D1.4M. If AWS D1.4 is not followed for manual arc welding reinforcing steel, the structural integrity of reinforced concrete may be jeopardized. Unfortunately, this particular contractor did not conform to D1.4 and the reinforcing steel was encased in concrete before a visual inspection could be conducted. This article covers AWS requirements for welding reinforcing steel in reinforced concrete applications. It summarizes the main themes of the various sections as they pertain to welding reinforcing steel and contains guidelines for working with the body of rules and procedures for structural welding of reinforcing steel to reinforcing steel, welding reinforcing steel to structural steel, and welding reinforcing steel to electrical grounding electrodes. Implications to improve future projects are also addressed. Fusion welds in shop fabrication of reinforcing steel and CADWELDs are outside the scope of this article. Electric resistance welds found in the fabrication process of welded-wire reinforcement are conducted by computer controlled welding machines within a controlled environment. A combination of pressure and heat generated by electric impulses fuse intersecting wires together. Shop personnel are never engaged in the actual welding process and no filler material or other foreign matter is introduced. CADWELDs do not apply because the steel-filled coupling sleeve of a CADWELD is a mechanical splice in which molten metal interlocks the grooves inside the sleeve with the deformations on the reinforcing bar. Weldability of reinforcing steel and compatibility of welding procedures need to be considered and closely supervised when manual arc welding of reinforcing steel is required. Weldability is determined by the chemical composition of steel and described by the Carbon Equivalent (CE) number. Carbon is the primary hardening element in steel. Hardness and tensile strength are inversely related to ductility and weldability. As carbon content increases up to 0.85%, so does hardness and tensile strength. As carbon
content decreases, ductility and weldability increases. CE is an empirical value in weight percentages, related to the combined effects of different alloying elements used in making carbon steel, of an equivalent amount of carbon. This value can be calculated using a mathematical equation. The lower the CE value the higher the weldability of the material. The welding Code provides two expressions for calculating CE. The first expression (Equation 1) only considers the elements carbon and manganese, and is to be used for all bars other than ASTM A706 material. A second more comprehensive equation (Equation 2 ) is given for ASTM A706 and considers carbon, manganese, copper, nickel, chromium, molybdenum, and vanadium content. Chemical composition is obtained through certified mill test reports or independent chemical analysis. Chemical composition varies for each production run, so it is important to obtain the analysis that matches the specific material to be welded. Once the CE number is calculated, the minimum preheat and interpass temperature is determined from Table 5.2 of the Code. If material test reports are unavailable and chemical composition is not known, which is particularly common in alterations and building additions of existing structures, the Code prescribes the highest preheat and interpass temperature for desired reinforcing bar size: 300° F (150° C) for number 6 bars and smaller, and 500° F (260° C) for number 7 bars and larger. If the chemical composition for ASTM A706 is not known or obtained, then preheat and interpass requirements are somewhat relaxed; no preheat is required for number 6 bars and smaller, 50° F (10° C) for number 7 to number 11 bars, and 200° F (90° C) for number 14 and larger. As with all welding, when the material is below 32° F (0° C), the Code prescribes the material to be preheated to at least 70° F (20° C), and maintained during the welding process.
ConstruCtion issues discussion of construction issues and techniques
Welding Reinforcing Steel AWS D1.4/D1.4M:2011 By John Hlinka, P.E.
John Hlinka, P.E., is Senior Project Manager/Structural Engineer at QualEx Engineering in Paducah, Kentucky. He can be contacted at jhlinka@qualex.com.
CE = %C + %Mn/6 (Equation 1) CE = %C + %Mn/6 + %Cu/40 + % Ni/20 + %Cr/10–%MO/50–%V/10 (Equation 2) Standard specifications for low-alloy steel ASTM A706 limit chemical composition and CE to enhance weldability. However, it is permissible to weld other base metals, such as ASTM A615, which is commonly used in reinforced concrete, as long as the appropriate weld procedure specification (WPS) is followed and correct filler weld metal is used. Many other permissible base metals are listed under paragraph 1.3.1 of the Code. High strength reinforcing steel such as ASTM A615 material is susceptible to cracking when not adequately
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